i have an ulterior motive in offering to help you.
我主动提出要帮助你是有私心的。
the family was looking at me gingerly, as if my long stare at the table had exposed my ulterior motive to them.
一家人的目光小心翼翼,或许是他们觉察到我不怀好意地盯了餐桌很久。
at that stage they were not yet an 「item」, and one is entitled to wonder whether there might have been an ulterior motive in her persuading him to stay.